1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a color filter substrate for a transflective liquid crystal display (LCD) device and a method of manufacturing the same.
2. Discussion of the Related Art
In general, the liquid crystal display (LCD) device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer interposed between the two substrates. Each of the substrates includes an electrode and the electrodes of each substrate are also facing each other. Voltage is applied to each electrode and an electric field is induced between the electrodes. An alignment of the liquid crystal molecules is changed by varying the intensity of the electric field. The LCD device displays a picture by varying transmittance of the light according to the arrangement of the liquid crystal molecules.
Because the liquid crystal display (LCD) device is not luminescent, it needs an additional light source in order to display images. The liquid crystal display device is categorized into a transmissive type and a reflective type depending on the kind of light source.
In the transmissive type, a backlight behind a liquid crystal panel is used as a light source. Light incident from the backlight penetrates the liquid crystal panel, and the amount of the transmitted light is controlled depending on the alignment of the liquid crystal molecules. Here, the substrates are usually transparent and the electrodes of each substrate are usually formed of transparent conductive material. As the transmissive liquid crystal display (LCD) device uses the backlight as a light source, it can display a bright image in dark surroundings. Because an amount of the transmitted light is very small for the light incident from the backlight, the brightness of the backlight must be increased in order to increase the brightness of the LCD device. Consequently, the transmissive liquid crystal display (LCD) device has high power consumption due to the operation of the backlight.
On the other hand, in the reflective type LCD device, sunlight or artificial light is used as a light source of the LCD device. The light incident from the outside is reflected at a reflective plate of the LCD device according to the arrangement of the liquid crystal molecules. Since there is no backlight, the reflective type LCD device has much lower power consumption than the transmissive type LCD device. However, the reflective type LCD device cannot be used in dark surroundings because it depends on an external light source.
Therefore, a transfective LCD device, which can be used both in a transmissive mode and in a reflective mode, has been recently proposed. A related art transfective LCD device will be described hereinafter more in detail.
FIG. 1 is an exploded perspective view illustrating a related art transfective LCD device. The related art transfective LCD device 11 has upper and lower substrates 15 and 21, which are spaced apart from and facing each other, and also has a liquid crystal layer 23 interposed between the upper substrate 15 and the lower substrate 21.
A gate line 25 and a data line 27 are formed on the inner surface of the lower substrate 21. The gate line 25 and the date line 27 cross each other to define a pixel area “P”. The pixel area “P” includes a transmissive region “A” and a reflective region “B”. A thin film transistor “T” is situated at the crossing of the gate line 25 and the data line 27. In the pixel area “P”, a pixel electrode 19 is formed. The pixel electrode 19 is connected to the thin film transistor “T”.
Meanwhile, a black matrix 16, which has an opening corresponding to the pixel electrode 19, is formed on the inside of the upper substrate 15, and a color filter 17 corresponding to the opening of the black matrix 16 is formed on the black matrix 16. The color filter 17 is composed of three colors: red (R), green (G) and blue (B). Each color corresponds to each pixel area “P”. Subsequently, a common electrode 13 is formed on the color filter 17.
FIG. 2 is a schematic cross-sectional view of a related art transfective LCD device. FIG. 2 indicates a pixel area of the related art transfective LCD device. In the related art transfective LCD device 11, a transparent electrode 19a is formed on the inner surface of a lower substrate 21 and an insulating layer 30 is formed on the transparent electrode 19a. A reflective electrode 19b, which may be a reflector, is formed on the insulating layer 30, and the reflective electrode 19b has a transmissive hole 20 corresponding to a transmissive region “A”. As stated above, the lower substrate 21 includes a gate line (not shown), a data line (not shown) and a transistor (not shown) thereon.
An upper substrate 15 is spaced apart from and facing the lower substrate 21. A color filter 17 is formed on the inner surface of the upper substrate 15. A common electrode 13 is formed on the color filter 17. Though not shown in the figure, a black matrix is formed between the upper substrate 15 and the color filter 17.
A liquid crystal layer 23 is disposed between the upper and lower substrates 15 and 21, and molecules of the liquid crystal layer 23 are arranged horizontally with respect to the substrates 15 and 21.
Polarizers (not shown) are arranged on the outer surface of the upper and lower substrates 15 and 21. The transmission axes of polarizers are perpendicular to each other.
A backlight 41 is located under the outside of the lower substrate 21. The backlight 41 is used as a light source of a transmissive mode of the transflective LCD device.
In the transmissive mode, a first light “L1” from the back light 41 penetrates the transparent electrode 19a in the transmissive region “A”. Next, while the first light “L1” passes through the liquid crystal layer 23, the transmittance of the first light “L1” is controlled by adjusting the arrangement of the liquid crystal depending on applied voltage.
On the other hand, in a reflective mode, a second light “L2” incident from the outside such as sunlight or artificial light passes through the liquid crystal layer 23 and is reflected at the reflective electrode 19b in a reflective region “B”. The second light “L2” passes through the liquid crystal layer 23 again and is emitted. At this time, the amount of emitted second light “L2” is controlled according the arrangement of liquid crystal molecules.
In the transflective LCD device, the color filter 17 is made of a material such as a pigment, which has a very low absorption coefficient of light in a specific wavelength range while it has a high absorption coefficient of light in other ranges. Therefore, light passing through the color filter has a color of R, G, or B according to a property of the pigment.
The first light “L1” and the second light “L2” have a difference in color when emitted. This is because the first light “L1” passes through the color filter only once while the second light “L2” passes through the color filter twice. Accordingly, the second light “L2” has higher color purity than the first light “L1”.
Additionally, there is a light glare effect in the transflective LCD device. This happens when a high-intensity external light source is reflected on a liquid crystal display panel. The displayed image is poor due to the glare that occurs as viewed by an observer due to the reflection of light. Therefore, a reflective electrode of an uneven shape and a front scattering film is suggested to increase the brightness along the normal direction and to decrease the light glare effect phenomenon.
FIG. 3 is a schematic cross-sectional view of a transflective liquid crystal display (LCD) device according to a first embodiment of the related art and FIG. 4 is a magnified view of the region “C” of FIG. 3. FIG. 3 shows only a reflective region of the transflective LCD device. In FIGS. 3 and 4, a pixel electrode 19 is formed on an inner surface of a first substrate 21. The pixel electrode 19 is composed of a transflective electrode 19a and a reflective electrode 19b, and an insulating layer 30 is disposed between the transflective and reflective electrodes 19a and 19b. As shown in FIG. 4, the insulating layer 30 has an uneven surface, so that the surface of the reflective electrode 19b is also uneven.
A second substrate 15 is disposed over the first substrate 21 and spaced apart from it. A color filter 17 and a common electrode 13 subsequently are formed on an inner surface of the second substrate 15. Though not shown in the figure, a black matrix is also formed on the inner surface of the second substrate 15.
In the transflective LCD device of FIGS. 3 and 4, the uneven surface of the reflective electrode 19b results in diffused reflection of the incident light “L3” minimizing specular reflection. Accordingly, a brightness along a normal direction of the reflective LCD device increases by changing a reflection angle of light
The uneven shape of the passivation layer is initially formed to have a square shape. Subsequently, the passivation layer is cured to form a round shape. Uniform curing of the entire area of the passivation layer is difficult because it is dependent on the curing conditions. The curing temperature may range from about 100° C. to about 200° C. As a result, the uneven shape is not uniform throughout the entire area of the passivation layer. It is difficult to increase a brightness of a reflective LCD device even using a reflective electrode of an uneven shape due to a smaller effective scattering area of the light on the surface of the substrate. Therefore, because the uneven surface is formed through a complicated process, the production yield decreases.
FIG. 5 is a schematic cross-sectional view of a transflective LCD device according to a second embodiment of the related art. FIG. 5 shows only a reflective region of the transflective LCD device. In FIG. 5, a pixel electrode 19, which is composed of a transflective electrode 19a and a reflective electrode 19b, is formed on an inner surface of a first substrate 21. An insulating layer 30 is disposed between the transflective and reflective electrodes 19a and 19b. 
A second substrate 15 is disposed over the first substrate 21 and spaced apart from it. A color filter 17 and a common electrode 13 subsequently are formed on an inner surface of the second substrate 15. Though not shown in the figure, a black matrix is also formed on the inner surface of the second substrate 15. A scattering layer 16 is formed on an outer surface of the second substrate 15 and a polarizer 22 is formed on the scattering layer 16.
The scattering layer 16 diffuses not only incident light “L3” but also reflected light “L4”, so that the brightness and viewing angle of the reflective mode increase. Besides, a process of forming the scattering layer 16 is simpler than that of forming the reflective electrode 19b having the uneven surface of FIGS. 3 and 4. However, since the scattering layer 16 is formed also in the transmissive area, the contrast ratio of the transmissive mode decreases, so that the quality of picture is poor.